The Gray square is the "ground" level.The green octagon is the water level.The white square is inside the invisible barrier.

The pictures below show the mapping process... look VERY carefully for the green arrow...

The player needs to push himself through the invisible barrier.To do this, he must make a little space between the hog and the invisible wall. Then he should toss a plasma grenade on the back of the hog and use the explosion to push the hog. The hog will push the player through the wall.